The invention relates to optical communication, and, more particularly, to generation and coherent detection of 400-Gb/s single-channel optical signal.
It is anticipated that a 400 Gb/s (Gigabit per second) per channel is a possible bit rate for long-haul (LH) optical transmissions, after 100 GbE (Gigabit Ethernet). In recent years, a lot of exciting results on 100 GbE LH optical transmissions have been achieved. However, there is no experimental demonstration of 400 Gb/s single-channel optical signal transmission. To generate a single carrier 400-Gb/s optical signal, even if polarization diversity (PD) and 16QAM modulation format are employed, the baud rate per carrier still goes up to 50 Gig baud/s, with no consideration to forward error correction FEC. The bandwidth of an analog-to-digital converter (ADC) chip at this rate is not available in the near future. Also, the transmission distance of this single carrier is short due to high optical signal-to-noise ratio (OSNR) requirements. To use multiple peaks or multiple subchannels to transmit a high-bit rate is a good solution to reduce the baud rate and extend the transmission distance. A 100-Gb/s transmitter with two peaks to tolerant large polarization mode dispersion and fiber dispersion has been demonstrated. Recently, a 100-Gb/s signal with a spectral efficiency of 2 b/Hz/s over 6000 km, with two peaks of an optical OFDM signal and Raman amplification, was demonstrated. It has also been demonstrated that a 100-Gb/s PD-RZ-QPSK (polarization diversity- return-to-zero-quadtrature phase shift keying) signal has good receiver performance at 25-GHz channel spacing. However, all of these 100-Gb/s demonstrations fall short of the capacity that a 400-Gb/s single channel system could achieve.
It is advantageous to further improve the design of optical communication with the